This is a study of a dynamic cohort of 13 250 commercial research and development personnel for whom information on occupational and educational background and smoking was available. Their age-, sex-, race-, and period-adjusted death rates were compared with New Jersey rates and with an internal comparison population. The overall results were favorable. The study groups had significantly fewer deaths from most major disease categories compared with other New Jersey residents. Among white male scientists and engineers, age-adjusted overall mortality and ischemic heart disease mortality were comparable to white male managers and support staff studied, whereas mortality from leukemia and lymphatic cancer was significantly elevated. Mechanics, however, had a significantly lower leukemia and lymphatic cancer mortality rate than did the comparison group. In a Poisson regression model in which white males and females from the study population were used, and for which the effects of age, smoking, college education category, period of hire, and years employed were controlled, scientists, engineers, and research technicians had elevated (nonsignificantly) mortality rates for leukemia and lymphatic cancer compared with managers and support staff. Smoking was an independent risk factor for leukemia and lymphatic cancer. Further work is needed to assess if specific environmental factors, such as benzene, other aromatics, radiation, medical treatment, and smoking habits, might have contributed to the above findings.